That's not true. He's tentative at times because he's young, but he never "quits". He has lazier possessions like any other NBA player would, but it probably has more to do with being unsure or tired than just "quitting".
He's done a great job, especially being the point man on a team with a bunch of veterans, he's also being asked to improve in other areas in terms of helping teammates and he has to work on balancing that with scoring. It would be nice for some pressure to be taken off of him at times as well.
He's a 19 year old kid, he's still years away from being to dominate every game in multiple facets night in and night out. He's learning, though. Scott is the perfect coach to have guiding him along the way.